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//! This module implements the `Attribute` struct which contains the attibutes for property descriptors.
use crate::gc::{empty_trace, Finalize, Trace};
use bitflags::bitflags;
#[cfg(test)]
mod tests;
bitflags! {
/// This struct constains the property flags as describen in the ECMAScript specification.
///
/// It contains the following flags:
/// - `[[Writable]]` (`WRITABLE`) - If `false`, attempts by ECMAScript code to change the property's
/// `[[Value]]` attribute using `[[Set]]` will not succeed.
/// - `[[Enumerable]]` (`ENUMERABLE`) - If the property will be enumerated by a for-in enumeration.
/// - `[[Configurable]]` (`CONFIGURABLE`) - If `false`, attempts to delete the property,
/// change the property to be an `accessor property`, or change its attributes (other than `[[Value]]`,
/// or changing `[[Writable]]` to `false`) will fail.
#[derive(Finalize)]
pub struct Attribute: u8 {
/// The `Writable` attribute decides whether the value associated with the property can be changed or not, from its initial value.
const WRITABLE = 0b0000_0001;
/// If the property can be enumerated by a `for-in` loop.
const ENUMERABLE = 0b0000_0010;
/// If the property descriptor can be changed later.
const CONFIGURABLE = 0b0000_0100;
/// The property is not writable.
const READONLY = 0b0000_0000;
/// The property can not be enumerated in a `for-in` loop.
const NON_ENUMERABLE = 0b0000_0000;
/// The property descriptor cannot be changed.
const PERMANENT = 0b0000_0000;
}
}
// We implement `Trace` manualy rather that wih derive, beacuse `rust-gc`,
// derive `Trace` does not allow `Copy` and `Trace` to be both implemented.
//
// SAFETY: The `Attribute` struct only contains an `u8`
// and therefore it should be safe to implement an empty trace.
unsafe impl Trace for Attribute {
empty_trace!();
}
impl Attribute {
/// Clear all flags.
#[inline]
pub fn clear(&mut self) {
self.bits = 0;
}
/// Sets the `writable` flag.
#[inline]
pub fn set_writable(&mut self, value: bool) {
if value {
*self |= Self::WRITABLE;
} else {
*self |= *self & !Self::WRITABLE;
}
}
/// Gets the `writable` flag.
#[inline]
pub fn writable(self) -> bool {
self.contains(Self::WRITABLE)
}
/// Sets the `enumerable` flag.
#[inline]
pub fn set_enumerable(&mut self, value: bool) {
if value {
*self |= Self::ENUMERABLE;
} else {
*self |= *self & !Self::ENUMERABLE;
}
}
/// Gets the `enumerable` flag.
#[inline]
pub fn enumerable(self) -> bool {
self.contains(Self::ENUMERABLE)
}
/// Sets the `configurable` flag.
#[inline]
pub fn set_configurable(&mut self, value: bool) {
if value {
*self |= Self::CONFIGURABLE;
} else {
*self |= *self & !Self::CONFIGURABLE;
}
}
/// Gets the `configurable` flag.
#[inline]
pub fn configurable(self) -> bool {
self.contains(Self::CONFIGURABLE)
}
}
impl Default for Attribute {
/// Returns the default flags according to the [ECMAScript specification][spec].
///
/// [spec]: https://tc39.es/ecma262/#table-default-attribute-values
fn default() -> Self {
Self::READONLY | Self::NON_ENUMERABLE | Self::PERMANENT
}
}